Hello!
I'd say its absolutely fine to include Forage programmes on your CV - especially early on when you might not have a long list of commercial experience yet. If the firm has specifically asked for them, I'd definitely include them to show initiative and genuine engagement with the profession.
In terms of listing virtual open days and events on your CV, it might be easier to put these in a separate sort of "events" section, or group them all under one heading in the work experience section.
You can definitely list Forage programmes and events in your work experience section, particularly if you can share particular insights that you gained. However, as above, you might find it helpful to group some of them together if you are struggling to write a lot about them.
As for verification, law firms generally don't "check" Forage experiences as far as I am aware, but you should always be ready to talk about what you learned and the tasks that you completed. As long as you are honest, you'll be absolutely fine